Let me guess - the Assembly folder appears empty to you, which is why you think "they didn't include whatever was in it". Am I right?
Actually, there's a desktop.ini inside the assembly folder that makes Explorer hide all its contents. Deleting that desktop.ini will reveal them all.
It has nothing to do with the Assembler language, but it contains all the core files of Microsoft's .NET runtime (from version 2.0 up to 4.x).